Thermostatic element



Feb, 19, 1935. N. 1'.. DERBY. 1,991,495 l THERMOSTATIC ELEMENT Filed Nov. 1, 1930 '4 sheets-sheet. 1

1995.191935.v mbH-BYy 1,991,495

THERMSTATIC ELEMENT Filed Nov. 1, 1930 4 sheets-sheet 5 5y 0125, Mfff #frans/Er Feb. 19, 1935. N. L. DERBY 1,991,495

THERMOSTATIC ELEMENT V Filed Nov. 1, 1950 4 sheetsy-sheet 4 'Patented Feb. 19.19.35' A i I' UNITED STATES PATENTA OFFICE 'rnEnMos'rA'rrc nLmmNr Norman I..V Derby, New York, N. Y.

ApplicatonNovember l, 1930, Serial No. 492,7 1a claims. (ci. 297-15) Thisinvention relates to thermostatic elements. Fig. 10 is a sectional view of a deeply corru- An object of this invention is to furnish an imgated tube made from the tubing of Fig. 9. proved thermostatic element that will contract Fig. 11 is a perspective view of a bimetallic and expand longitudinally in response toachange tube comprising three superposed tubes joined I in temperature. permanently together. v Another object of this invention is to furnish 12 is a sectional view of a deeply corruautomatic devices utilizing a thermostatic elegated tube constructed of the tubing of Fig. 11. ment that will expand or contract in a generally .having sections of its inner and outer surfaces longitudinal direction in response to a change in removed to make the tubing eXPaDd and COIltraCt temperature. in response to a change in temperature. l0

Another' object is to furnish an improved ther- Fig. 13 is a perspective view of another type of mostjatic element with alternate portions having thermostatie tubing. the'WallS 0f Which Will eX- relatively high electric conductivity while therepand or collapse in reSDODSe t0 a' Change in temmaining portions have a relatively low electric Dereture- 15 conductivity. Fig. 14 is a sectional view of the tubing shown 15 Another object of this invention is to furnish in Fig. 13 lillustrating themanner in which the a thermostatic element in which one of the metals tube collapses when heated. is continuous while the other metal is divided. Fig- 15 iS a perspective View 0f a Corrugated Another object of lthis invention is to furnish thel'mOStetie element having Portions Curved Aim an improved corrugated thermostatic element. transversely t0 the COrrllEetiOn Curves thereof 20 Of the drawings. to stien the element. Fig. 1 is a perspective view of a sheet of bime- Fig- 16 ,is e P1811 View and Fig'- 17 iS an end view tame stock from which the'thermostatic element of sectionsof a Sheet ofthermostatic stock simis made.' ilar to that shown in Fig.. 1 and Fig. 7.

i Fig, 2 is a perspective View of a thnostatic Fig. 18 is a section on the line 18^18 of Fig. 16, 25

element made from the stock of Fig. 1. 0f a corrugated strip shown atin Fie- 16.

Fig. 3 is an elevation in section on the line 3-3 v F18- 19 is en enlrged front View 0f 8 portion 0f of Fig. 3-A, of a quick opening and closing switch the strip shown in Fig. 18 after said strip has been included in an electric heating circuit and utilizdeeply COI'rUZeteding the new type of thermostatic element. F18- 20 1S en end View Qfthe Strip ShOWn in 30 Fig. 3-A'is an end view of the switch shown F18. 19. in Fig. 3. v f Fig. 21 is a front view of a corrugated strip Fig. 3-B is an end elevation of the switch with Shown mit in Fi8 16 in which the cerrllgation the thermostatic element in section on the line grooves are 0f helical form.

A 3B-3B of Fig. 3. Fig. 22 is an end view of the strip shown in 35- Fig. '4 is a perspective view of a sheet of ther- Fig. 19. l mostatic stock diiering slightly in construction The usual type of commercial bimetallic ele?- fmm that shown in pig, 1, in that the invar con. ment consists of two continuous strips of metal necting sections'are widen having widely diiering coeiiicients of heat exl 40 im. A is a View similar mms. 4 showing a 'pans1on. usually brass and invar -steel joined 40 slightly different construction of thermostatic remleanmtmwhtggeoher gime xatedms. mtspet rrug ted w no mvvendfh sections .of the upper and lower layers expand longitudinally, but rather, will tend to l coil into a circular form. The 'element which is 4f ifissrzrritineraire @he :they as man-wm mand f Fig. Band Fig. 'Z are perspective viewsillustrattperglgrimdmauy in to Ia' change of mgthe foxfxriation of sheet stock by rolling down Referring to um draw-mss, pig; 1 shows a sheet a compoun ingOtof this new type of bimetallic themostatic stock.

Fig. 8/isa perspective view of the thermcstatic' Euh surface `shows alternate sections of theV 50 g element lcomprising two side by side corrugated 4two metals, the metal having a low coeihcient of strip sections. I heat expansion being invar steel and the metal. Fig- 9 iS a DerSDeetiVe View 0f e-tllbe enstruct- 'having' a high cqemcient of heat expansion being ed of bi-metallic sheet stock with a longitudinal lead free brass. Itwill be noticed that sections welded Joint. i Y of thesheet showing brass on the upper surface 55 will show invar on the under surface and likewise sections showing invar steel on the upper surface will show brass on the under surface. In the particular sheet of stock shown in Fig. l strips of brass are permanently joined to a continuous sheet of invar steel. ln Fig. 2 the sheet of 'stock Fig. 1 has been corrugated so that the brass sections come on the inside and the invar on the outside of the bends of the corrugations, and the seams are located on the sides of the corrugations half way between the lower and upper bends. The corrugated thermostatic element shown in Fig. 2 will expand longitudinally, or parallel to its length, when heated. However if the sheet of stock shown in Fig. l is corrugated so that the brass is on the outside of the bends and the invar on the inside of the bends the element will contract longitudinally instead of expanding when heated.

The preferred method of making the compound stock from which the corrugated thermostatic element is formed comprises forming a compound ingot as shown in Fig. 6 approximately l2" wide x 36" long x 1%" thick consisting of a slab of invar steel having longitudinal grooves which are iilled with brass, the brass being permanently joined to the walls of the grooves. The brass is preferably fused into the grooves by automatic arc welding.Y After the compound ingot is formed it is reduced in thickness, to say 1%" by cold rolling in the direction of its length as shown in Fig. 6. Then the reduced ingot is sheared into slabs, the first slab being sheared off on line A-B. This slab is then reduced to the finished thickness by' rolling in the opposite direction, that is, at right angles to the rst rolling operation. The second rolling operation is shown in Fig. 7.

After the last rolling operation the bi-metallic stock strip may be given the corrugated form shown in Fig. 2, by several sets of corrugating rolls, each succeeding set imparting deeper and narrower corrugations to the sheet of stock. Instead of corrugating rolls, a die similar to that used for making corrugated metalrooflng may be used to eorrugate the strip.

As is well known, the reduction by cold rolling imparts a grain to metal and the maximum strength is obtained by bending the metal at right angles to the grain. In the operation shown in Fig. 6 the grain formed is parallel to the length of the slab and in the operation shown in Fig. 7 the grain formed is in the transverse direction.` When a corrugated thermostatic element is formed from the finished stock of Fig. '1, the bends will be at right angles to the grain and give the element maximum strength to resist bending strains.

There are several other methods which may be used in forming the compound ingot. For instance strips of sheet brass coated with a iiux of borax may be located in a mold as cores, and molten invar .steel poured into the mold. The molten steel will melt a film of brass and when the ingot cools the brass will be fused to the walls of the grooves in the steel. Another method is to take a slab of rolled'invar, mill or die stamp longitudinal recesses in the slab to receive the brass, iill the recesses with a finely divided mixture of brass filings and borax, then melt said brass with an ordinary illuminating gas or acetylene torch, then grind the brass, united to the steel, level with the top of the steel, and then reduce the compound slab by rolling as previously .described Still another method is to solder strips of rolled brass into the recesses of the rolled invar with' silver solder and then reduce as before by rolling down the compound slab.-

In all the descriptions thus far the invar steel is represented as the continuous metal and the brass is represented as the divided metal. However this arrangement may be reversed in most cases. I may fuse molten invar steel into grooves in a slab of brass or Monel metal by arc Welding, preferably the atomic hydrogen type of arc welding, or strips of invar steel may be silver soldered into grooves in a brassslab. Fig. 5 represents this arrangement. It is to be understood that the term recess as used herein applies also to the recesses directly formed in one side of a thin sheet of metal by a die stamping operation directly forming spaced recesses or depressions in the opposite side of the sheet. A thin sheet of one metal so formed with a series of recesses at one side alternating with a series of recesses in its opposite side may have secured ln each of said recesses a layer or section of a diil'erent metal to thereby produce bimetallic stock material generally similar in form to that shown in Fig. 1.

Ordinarily, an element constructed in accord.

ance With the present invention and designed for carrying an electric current without much heating up, will have the metal ofhigh electrical conductivity as the continuous metal and the metal of lower electric conductivity as the divided metal. This arrangement is shown in the. sheet of stock Fig. 5. Conversely, where it is desired Y to utilize the heating effect yof an electric current passing through the thermostatic element to operate same, the two metals are preferably arrangedv as in Fig. 1 or Fig. 4, that is, with the high resistance invar steel continuous and the low resistance brass divided so that the current is compelled to pass through alternate portions of high and low resistance. The heating effect of "the current passing through the portion of invar may then be utilized to operate the element.

Invar steel having a very low coeilicient of heat expansion is the best metal now known to me y for use as the low expansion metal however, in lieu of brass numerous other metals may be used for the high expansion metal, especially where it is desirable to have a thermostatic element suitable for high temperatures. For instance Monel metal may be used with the-invar steel, or another steel, one having a high percentage of copper may be used with the invar steel to form thethermostatic element. A very good high exp ansion alloy for use with-invar has the following composition, 12-l5% nickel, 57% copper, 1.50-3% chromium, and the balance electrolytic iron. 1

All the methods of making the thermostatic stock thus far described, involve the insertionof one metal in grooves formed in a continuous sheet of the other metal, but in some cases, especially when the quantity of elements desired is small, it may be more economical to use a different procedurel in making corrugated elements. For example, as shown in Fig. 4-A, a slab of rolled invar may be permanently sandwiched between two slabs of rolled brass, the joint between adjacent surfaces being m'ade with silver solder or other suitable means. After a compound slab is thus formed it is cold rolled down parallel to its length to the desired thickness, and after the rolling operation, sections of the outer surfaces of brass are removed down to the steel.4 I

Then each surface will show alternate sections of brass and invar. In the constructionshown in Fig. vi---A as in those previously described, a

- show brass on the under surface. The sheet of stock shown in Fig. 4-A may be corrugated as previously described.

In forming the stock shown in Fig. 4-A the sections ofbrass may be removed in several ways,

' for example, they may be removed mechanically by milling or grinding, or chemically, by covering the sections of brass that lare to remain with an asphalt varnish, then dipping the sheet in a mixture of nitric acid and water having a specic gravity of 1.2. The acid will etch oil' the exposed sections of brass and leave remaining those sections oi brass protected with varnish. The acid will' not aifect the steel.- The brass sections may also be removed by electrolysis. In such case the sections of brass to remain are first 4protected with wax or shellac and then the sheet is placed as the anode in an electroplating solution. 'Ihe brass stripped of! will be deposited on some other object as the cathode. The electroplating solution is preferably 171/2 parts copper acetate, 22 parts potassium cyanide, 17% parts'sodium bisulphide, 211/2 parts sodium carbonate to 100 parts of water by weight. Twoor more corrugated thermostatic elements expanding and contracting in the direction of their lengths may advantageously be combined into a single thermostatic element in some cases, one such combination being illustrated in Fig. 8. The element shown in Fig. 8 comprises two similar corrugated strip elements 11 and 12 each rigidly attached at -one endto the corresponding end of the other through a connecting end portion 13. As shown in Fig.- 8,the opposite end portions 11a and 12a of the strip sections extend alongside of one another in the direction of the element, and are apertured for attachment to a part 14 such as a valve, switch contact or the like to be actuated. With each section thus connected at its opposite ends to the corresponding ends of the other section, each section reinforces the other against lateral bending. Advantageously the two sections are similar not only in shape but in disposition in that each individual corrugation or curved portion of each section is alongside a similar corrugation or curved section of the other section,

.and preferably-also the concave and convex sides of each corrugation or curved portion of one section faces in a direction opposite to that in which the concave and convex sides oi the alongside corrugation or `curved portion of the other section faces: So arranged each longitudinal portion of each section expands and contracts as does the alongside portion of the other section in response to a change in temperature which is advantageous in some-cases, as for instance, when diiferent longitudinal portions of the element are subjected to different temperatures.

The previous descriptive matter relates princip'aily to av thermostatic element made by corrugating ilat sheet stock. However the element may be constructed in the form of a deeply corrugated-tube either seamlessor with a welded joint. Fig. 9 shows a sheet -of stock like that shown in Figs. 1 and '1 bent into the form ofa,

' tube with a welded longitudinal joint c-d, preferably formed by atomic hydrogen arc welding the abutting strip edges. After the tube is made it may be deeply corrugated, as shown in Fig. 10,

, by any of the methods now in use for forming three layers permanently joined together, the middle layer being invar and the two outer layers being brass. In makingthe tube shown in Fig. 11, a compound hollow ingot is ilrst formed with the three layers joined together by fusion, and this ingot is cooled down to a thickness of wall suitable for corrugating and is then given the corrugated form as shown in Fig. 12. Sections of the brass represented by the dotted lines in Fig. 12 are removed either before or after the tubing has been deeply corrugated. The brass is removed either chemically or by electrolysis, in the -same manner as described previously for removing sections of brass iromthe ilat sheets. The deeply corrugated tubes shown in Figs. 10 and12 will contract or expand longitudinally in response to a change intemperature. Fig. 13 shows a thermostatic tube made up of a seamless tube of one metal like invar, recessed to receive segments of another metal like brass. 'I'he segments of brass are permanently joined to the invar, preferably by fuson,. and then the walls of the compound tubing reduced by cold drawing to the desired thickness. The tubing shown in Fig. 13 lwill collapse approximately into the shape shown in Fig. 14, when heated and will again return to its original shape when cool.

Fig. 15 shows another variation of the corrugated thermostatic element, in which the corrugations are bulged outwardly at the center to make the element more rigid, so that it will stand out horizontally, even if made of very thin stock, when supported at only one end.

The thermostatic element strip 20a shown in Fig. 16 may be cut in the manner indicated in Fig. 16 from thermostatlc stock sheet material like that shown in Fig. 7, and is characterized by the fact that the side edges of the strip are undulating with the concave and convex portions of one edge directly adjacent concave and convex portions respectively of the other edge, so that the width of the strip alternately increases and decreases along the length of the strip, and is further char-- -acterized bythe fact that the meeting surface edges of the two metals of the strip are inclined to the length vof the latter and are located in the narrow portions of the strip.

Fig. 18 shows a thermostatic element with shalfacing crests. The narrowing of said portions, 'which are subjected to bending stresses by the relative expansion of the layers in the wider crest portions, gives increased sensitivity in response to y temperature changes as compared with the elements previously described. The method of separating the strip 20a from the stock sheet material illustrated in F18. 18 obviously avoids waste in forming 'a multiplicity of said strips from the same sheet.

Using the same stock shown in Fig. 16, a thermostatic element -may also be made having helical corrugations therein and conforming in the form of its inner and outer surfaces to the surface of a segmento! a helical worm. 20h represents'a strip of stock cut out for this type of element. Fig. 2l is a front view of the helical corrugated element and Fig. 22 isaplan view of this element. A helical corrugated element of this type can best be formed by using a worm andv worm gear with the proper clearances as the forming dies.

Fig. 3 represents in section an electric heating device, such as an electric heating iron, having a heating element (1), and a quick opening and closing thermostatic switch (2), the element l being a resistor in an electric heating circuit including a source of current (10). The switch shown in Fig. 3 comprises a corrugated thermostatic' element 2a anchored at one end and carrying a switch contact 5 at its free end, and a cooperating switch contact 4 carried at the free end of a screw 7 threaded into a supporting anchorage adjacent the anchorage end of the element The latter is formed adjacent its free end with a spring tongue or latch part 3 cooperating with spaced apart latched recesses formed in the insulator 8 which is carried by the screw 7 and carries the contact 4 in Fig. 3. When the temperature of the surrounding atmosphere drops to a predetermined point the corrugated thermostatic element 2a contracts and the latch 3 deflects out of one of said latch recesses into the other causing a snap contact between contacts (4) and (5) and thus completing the circuit. As the surrounding temperature becomes too high the thermostatic element again tends to expand longitudinally. The force exerted on latch (3) by the expanding element 2a causes the latch to deflect back into the latch recess initially occupied and contact between (4) and (5) will be broken with a snap action. The arrangement of the partly cut out thermostatic section (6) of the element 2a is such that it willA tend to hold the contact tight until broken with a snap and likewise section (6) tends to prevent the contact from taking place until it can do so with a snap action. The thermostatic switch can be set for any desired operating temperature by adjusting screw (7). (9) is an electric insulator.

Having described my invention what I vclaim and desire to secure by Letters Patent is:-

1. A corrugated bimetallic thermostatic element of uniform thickness comprising a continuous sheet of one metal having recesses therein. and another metal permanently imbeddedin and lling said recesses and having acoefcient of expansion different from that of the rst'mentioned metal.

2. A thermostatic element oi uniform thickness comprising a continuous piece of recessed metal and inserts of another metal permanently united to the walls of and completely filling the recesses in said first mentioned metal, the two metals having different coeicients of expansion. l

3. A thermostatic element comprising a rolled sheet of uniform thickness including a continuous web of one metal `alternately recessed at opposite sides of the sheet and sections of another metal, said metals having diil'erent coeiiicients of expansion, iilling said recesses and integrally connected to the said web. i

4. A thermostatic element comprising a rolled sheet of uniform thickness including a continuous web of one metal alternately recessed at opposite sides of the sheet and sections of another met-- al, said metals having different coefiicients oi' expansion, filling said recesses and integrally connected to the said web, said sheet being bent into a structural form the shape of whichl is distorted in a` predetermined manner by the unequal expansion of the different metals on changes in the temperature thereof.

5. A thermostatic element comprising a rolled sheet of uni'orm thickness including a continuous web of one metal alternately recessed atopposite sides oi the sheet and sections of another metal, said metals having different coeiiicients of expansion; filling said recesses and integrally.

connected to-the said web, said sheet being formed with alternate bends with one metal exposed at the convex side and the other metal exposed at the concave side of each bend.

6. A corrugated bimetallic thermostatic element consisting of sheet material of uniform thickness including a number of similar and similarly proportioned corrugation loop portions extending ih one direction andalternating with an equal number of loop portions similar in number and proportions to the rst mentioned portions and extending in the opposite direction, each of said loops comprising an inner layer of metal having one coeilicient of expansion and an outer layer of another metal having a different coeflltient of expansion.

7. A bimetallic thermostatic element in the form of a strip of corrugated sheet material the corrugation loops of which comprise an inner layer of metal having one coeflicient of expansion and an outer layer of another metal having a different coefiicient of expansion, the sheet material being curved transversely to the length of the element to increase its transverse stiffness.

8. A bimetallic thermostatic element in the form of a strip of corrugated sheet material the corrugation loops of which comprise an inner layer of metal having one coemcient of expansion and an outer layer of another metal having a different coefllcient of expansion, the loop crest portions of said strip being wider than the intervening portions of the strip. Y

9. A bimetallic thermostatic velement in the form of a corrugated strip of sheet material comprising integrally connected sections of metals having diierent coeilicients of expansion so arraged that exposed portions of one metal alternate with exposed portions of the other metal at -each side of the sheet and veach of said portions exposed at one side of the sheet is in juxtaposed relation with a portion of different metal exposed at the other side of the sheet with the meeting edges of the adjacent portions 'exposed at each side of the sheet inclined to the length of the strip and included in the strip portions which connect oppositelyextending corrugation loops.

10. A thermostatic element comprising two similar side by side strip sectionseach rigidly connected at each end to the corresponding end of the other and each including one or more curved portions alongside a corresponding curved portion of the other section, the concave and convex sides of each such curved portion facing in directions opposite to those respectively faced by the concave and convex sides o1' the adjacent curved portion of the other section, each such curved portion comprising a. layer of one metal at one side and an integrally connected layer of a different metal at its opposite sides, one of said layers having end portions extending beyond the ends oi the other layer and layer portions of the same metal as the last mentioned layer integrally connected to said end portions at the sides oi' the latter remote from the last mentioned'layers, said metals having different coeillcients of expansion whereby a change in the temperature of the element causes the two ends oi' each section to move .toward or away'from one another.

1i. A thermostatic element comprising two similar side by side strip sections each'rigidly connected lat one end to the corresponding end of the other and each including one or more curved portions alongside a corresponding curved portion of the othery section, each such curved portion comprising a layer of one metal at one side and an integrally connected layer of a different metal at its opposite sides, one of said layers having end portions extending beyond the ends of the other layer, and layer portions of the same metal as the last mentioned layer integrally connected tosaid end portions at the sides of the latter remote from the last mentioned layer, said metals having different coeicients of expansion whereby a change in the temperature of the element causes the two ends of each section to-move toA Ward or away from one another.

12. Althermostatic element comprising an extended body comprising4 rigidly connected portions of materials having diierent coefficients of expansion compressed into a thin sheet curved and having smooth surfaces without joint cracks and with a series of portions exposed at each surface and with the materials o1 each v'portion so ex- 'posed having a. different coei'llcient of expansion from that of the material of an adjacent portion, and with the material of each portion exposed at one surface having a -derent coefiicient of expansion from the material in the juxtaposed por-v tion exposed at the other surface.

13. A thermostatic element formed from a body comprising integrally connected portions of metal having different coefcients of expansion and adapted to be tempered by working operations, and compressed to reduce the thickness of said body and convert it into a thin sheet having smooth side surfaces at each of which is exposed a series of portions of metal so disposed that the metal of each portion exposed at each side of the sheet has a different coeiiicient of expansion from that of the metal of an adjacent portion exposed at the same side of the sheet and so that the metal of eachportion exposed at one side or the sheet NORMAN L. DERBY.

has a different coefficient of expansion from that 20 

